(290c) Case Study of a Greener pH Swing Crystallization In a Double Feed Stirred Reactor

An industrial crystallization system was analyzed using a green engineering approach. The current method to crystallize a metal catalyst uses a stirred reactor, where an acid solution is added to the mother liquor to precipitate the catalyst in a semi-batch fashion. A double-feed reactor configuration was also examined and found to improve this process. This new scheme reduces the turnaround batch time by 90% and the environmental impact by 30% (LCI metrics), compared to the current single-feed operation scheme. The experiments showed that operating in a double feed mode allowed the crystallization to be conducted at a constant pH which resulted in a high purity, larger particle size. From this, a high settling velocity was achieved and resulted in a reduction in batch time. Additional experiments showed a relationship between the pH and the size of the agglomerates and the purity of the crystals. Further research on the crystallization mechanism and kinetics is strongly recommended for the generalization of the concept found in this investigation or its application as a continuous process.